Introduction to Operating Systems and Their Functions

Operating System (O/S)

- Programs that integrate hardware resources of computer

- Makes resources available to user efficiently

Efficiency in O/S is measured through...?

1. Functionality

2. Performance: Time and Utilization

3. Convenience and Cost

OS is a layer of _______ between ___ and _____

layer of abstraction between the hardware and software

OS Role

1. Resource Coordinator

2. Virtual machine

3. Reactive system

Operating Systems Ease the Pain

Performs interface task w/ hardware (file operations, memory paging) which the user does if OS didn't exist

The OS makes visible the _______ component of the system

virtual

The O/S does the ff. except...

A. Middleman between hardware and software

B. Resource divider

C. Reactive system

D. Being a real machine

D. Being a real machine

It's a virtual machine

Multiuser Capability

Multiple users can access resources at the same time

Interaction of Programs and Other Apps

OS allows program interaction with different applications

Why are Operating Systems Difficult to Create and Maintain?

1. Size

2. Lifetime

3. Complexity

4. Multitasking

5. General purpose

OS Difficult to Create and Maintain: Size

- Too big for one person

- Current systems have so many lines of code and involve 10-100 man years to build

OS Difficult to Create and Maintain: Lifetime

- OS remain longer than the makers

- Code is written and rewritten so original intent is forgotten

OS Difficult to Create and Maintain: Complexity

System do difficult things:

- deal w/ ugly I/O devices

- multiplexing / juggling act

- handle errors

OS Difficult to Create and Maintain: Multitasking

Do several tasks at once

Early 1950's, Mainframes Rule

- Early systems

- No O/S

- Programmer = operator

- Large machines run from a console

- Programs loaded via switches & card readers

What were the first real OS?

Simple batch systems

Batch Processing

- O/S was a program stored in one part of memory

- Loads a job from card reader into memory

- Transfers control from one job to the next

Problem in Batch Processing

- Setup time

- Operators hired, ran related jobs together (very labor intensive)

Offline Processing

- Tape contains code

- Tape is read but don't know what output tape says

- Only see output after tape is read

What does spool stand for?

Simultaneous Peripheral Operation On-Line

Spooling

- Jobs can be read ahead onto disk

- Read line by line

Multiprogrammed Systems

- Increased utilization

- Keeps several jobs in memory simultaneously

- Needs CPU scheduling

- Analogy: lawyer working on several cases

Multiprogrammed Systems Overlapping of jobs

I/O processing of a job overlaps w/ computation of another job

Timesharing System optimizes ____?

Reponse Time

All computers have same efficiency and throughput so processor memory is divided among computers

Timesharing System is based on ____?

Time-slicing

Dividing CPU time among multiple processes

Timesharing System

Allows multiple users to interact with a single processor

Desktop Systems

- First appeared in 1970

- Popularly known as personal computers (PCs)

- Advancement in hardware allowed downsizing from expensive mainframes

Multiprocessor Systems is also known as ___?

Parallel systems

Tightly-coupled systems

Multiprocessor Systems

• Systems with multiple CPUs working together

• Can be Asymmetric or Symmetric

Advantages of Multiprocessor Systems

1. Increased throughput (more CPUs = more work in less time)

2. Economy of scale (saves money, CPUs share peripherals)

3. Increased reliability (redundancy and fault tolerance)

Asymmetric Multiprocessing

each CPU has specific role (usually master-slave)

Symmetric Multiprocessing (SMP)

All CPUs do same thing

Multicore System

Instead of multiple processors in 1 set up, processors are divided into cores (each with own cache line) for tasks

Distributed (Loosely-Coupled) Systems

CPUs assigned specific roles in processing.

What does Distributed (Loosely-Coupled) Systems allow?

- Geographically-distributed computing resources

- Communications between parts of a job or diff. jobs

- Resource sharing

Client-Server Systems

Architecture where clients request services from servers

Peer-to-Peer Systems

Decentralized network where each node shares resources

What kind of architecture is Distributed (Loosely-Coupled) Systems?

Peer-to-peer systems

Clustered Systems

- Multiple CPUs linked and collab to perform tasks

- Shared storage (data) via LAN

Real Time Systems

Systems responding to physical events within fixed time

Applications for Real Time Systems

• subway systems

• flight-control

• factories

• power plants

Problems with Real Time Systems

Need to schedule activities to meet time constraints

Hard Real Time System

Critical deadlines for controlling devices

Soft Real Time System

Important deadlines, less critical than hard systems.

Handheld Systems

PDAs and cellphones

Problems with Handheld Systems

1. Limited main memory

2. Processor speed

3. Small display screens

General Structure of an O/S: 2 types of programs

1. Resident

2. Non-resident

Resident Programs

• Programs which are critical to the operation of the system

• Embedded in system

• Allow PC to work

Non-Resident Programs

• Programs loaded into memory as needed

• Located in disks or bulky storage devices

Kernel

• Computer program in core of computer OS

• Complete control over everything in the system

• Prevents and handles conflicts between processes

Examples of Kernel that are memory resident components

1. Command interface shell

   eg. ver, dir, date, time: COMMAND.COM

2. I/O routines that control I/O devices

   e.g. BIOS: IO.SYS

3. File Management System

   e.g. MSDOS.SYS

Examples of Kernel that are non-resident components

• FORMAT, FDISK

• Stuff you plug to OS

Dual-Mode Operation

System operates in user and kernel modes

User Mode

System executes task for user

Kernel Mode

- System executes task for OS

- Executes privileged instructions

- Default at boot time

Privileged Instructions

Special instructions only executable in kernel mode

Bit changes depending on the mode

0 = go to kernel

1 = returns to user

If you request an O/S service, which is correct?

A. User to Kernel

B. Kernel to User

A. User to Kernel

8 OS Components

1. Process management

2. Main memory management

3. File management

4. I/O system management

5. Secondary storage management

6. Networking

7. Protection System

8. Command Interpreter System

Process management

- create

- delete

- suspend

- resume processes

- synchronize communications

- handle deadlocks

- possible support threads

Main Memory Management

• Tracks memory use

• Allocates / deallocates memory

• Decide which processes to load when there’s available space

File Management

• Tracks available space

• Maintains file info and directory structure

• Support file manipulation commands

I/O System Management

- Allows access to devices

- Use of device drivers for modularity

Secondary Storage Management

- Storage allocation

- Free space management

- Disk scheduling

Networking

- Transfer protocols

- Routing & connection strategies

Protection System

- Mechanism for controlling access to programs, processes, or users

- For multitasking and multiuser systems

Command Interpreter System

User interaction via command line, GUI, touch, voice, etc.

OS Architectures

1. Monolithic

2. Layered

3. Virtual Machine

4. Microkernel

Which O/S architecture is the easiest to implement?

Monolithic

Monolithic Architecture

- Virtually no structure

- Kernel = 1 big structure

- Procedures visible to each other

Layered Architecture

- Hard to implement bc functionalities are mutually dependent

- Inefficient bc many traversals

- Many checks to pass bc many layers to reach destination

Virtual Machine Architecture

- Many systems in 1 machine

- No resource management and responsiveness

Order of parts in

Virtual Machine Architecture

process -> kernels -> virtual machine -> hardware

- This allows things to run very fast

Microkernel Architecture

• Takes as much functionality as possible from kernel

• Allows modularity and portability across platforms

• Efficient

• Small monolithic kernel but user & system processes divided into user mode

Architecture of Systems Today

• Monolithic w/ hybrid of microkernel

• Non OS components controlled by user instead

When and where was the first version of Unix developed?

(1969)

Research Group in Bell Labs

Who developed the 1st version of UNIX?

Ken Thompson

What hardware was used to create UNIX?

PDP-7 (which was idle at that time)

Who joined Ken Thompson?

Dennis Ritchie (worked on MULTICS)

What hardware did Ritchie and Thompson use to create the 2nd version?

PDP-11/20

What did Ritchie and Thompson use for the 3rd version of UNIX?

C (developed in Bell Labs to support Unix) instead of assembly language

What enhancements were added to UNIX in version 4/5?

• Multiprogramming

• Run multiple programs at the same time

What hardware did Ritchie and Thompson use for the 4th/5th version of UNIX?

PDP-11/45 and PDP-11/70 (both support multiprogramming)

Version 6 Unix

(1976)

1st version distributed outside of Bell Labs

Version 7 Unix

(1978)

- Ancestor of most Unix systems

- Ported to VAX (appeared as 32V)

What hardware was used for version 7 of UNIX?

Developed for the PDP-11/70 and Interdata 8/32

Who produced the 3BSD Unix?

Bill Joy & Ozalp Babaoglu

Berkeley Software Distributions (BSD)

- 1st implementation of such functionality

- Allowed big programs to run in Unix

DARPA

Defense Advanced Researched Projects Agency

4BSD

Goal: Provide networking for DARPA Internet networking protocols (TCP/IP)

4.2BSD Release

- Communicate among diverse network facilities (LANs, WANs)

- New user interface = C shell

- New text editor = vi

4.2 BSD in 1984

60 connected networks

4.2 BSD in 1993

8,000 connected networks, 10 million users

What was the last Berkeley release?

1993

4.4 BSD

4.4BSD Release

- x.25 networking

- new file system organization

- enhanced security

- improved kernel structure

Unix Standardization Projects

Efforts by IEEE, ISO, and ANSI for Unix environments.

Unix Design Principles focus

• Time-sharing system

• Allows multiple processes

• Simple

• Kernel provides some functionality

• Source code provided

Unix Design Principles later use

• Networking, graphics, real-time operation

• Needed a lot of code (double size of system)

• System remained Unix

Unix Shell

• Command interpreter

• Executes user-written and system programs

• Surrounds kernel

• Users can write own shell

Popular command line shells

Bourne shell (Steve Bourne)

C shell (Bill Joy, BSD systems)

Korn shell (Dave Korn, C & Bourne combo)